A few years ago I stood on still-warm aa lava recently erupted from a volcanic fissure in Iceland. Somehow that fissure, and others like it along the earth's ridge axes, are responsible for making two-thirds of the earth's crust, including almost all the Atlantic Ocean's floor. Standing on a fissure, I can't see how that process happens. Crustal formation starts 100 km under my feet, well below the depth to which informed speculation based on field geology can penetrate.

Hence, I rely mainly on seismic tomography techniques that form images of earth's deep interior in much the same way that physicians' CAT scanners probe the human body.

I have applied tomographic imaging techniques to ridge axes and volcanoes in Iceland, fault systems in California, and mountains in the Himalayas. I also have a long-standing interest in improving and extending data analysis techniques that underlie interpreting modern digital data. I am always asking whether we can make a new type of measurement - or process standard measurements in a novel way - to improve images of earth structures.